3.5 includes multiple abilities that redirect a portion of incoming damage to other creatures. For instance:
The psionic power Share Pain states:
You take half damage from all attacks that deal hit point damage to you, and the subject takes the remainder. The amount of damage not taken by you is taken by the subject.
Similarly, the Shield Self ability granted by the vestige Dahlver-Nar (Tome of Magic, p. 27) states:
...you can designate one creature within 10 feet per effective binder level to share the damage you take. As long as the subject creature remains within range, you take only half damage from all effects that deal hit point damage, and it takes the rest.
If a creature is protected from damage by more than one such ability, what happens?
- Do the effects stack additively, granting de facto immunity to hit point damage (each ability redirecting half of the incoming damage; 50% + 50% = 100%)?
- Do they stack sequentially/multiplicatively (50% of damage redirected by the first ability, then 50% of the remaining damage redirected by the second, resulting in the protected creature taking 25% of the incoming damage)?
- Do they not stack at all?